High frequency gyromagnetic device employing slot transmission line

ABSTRACT

A high frequency gyromagnetic electromagnetic wave transmission device has a symmetric structure including planar high frequency energy conductors defining a wave guiding slot, the conductors being based on a dielectric substrate and covered by a similar superstrate, in which the dielectric strata are formed with gyromagnetic toroids which may be excited to produce static magnetic bias fields for the control of the velocity of propagation of high frequency energy along the transmission device.

United States Patent Robinson et a1.

[i 3,707,688 [4 1 Dec. 26, 1972 [54] HIGH FREQUENCY GYROMAGNETIC DEVICEEMPLOYING SLOT TRANSMISSION LINE [72] Inventors: Gerald H. Robinson,Dunedin; Harry F. Strenglein, Clearwater, both of Fla.

[73] Assignee: Sperry Rand Corporation [22] Filed: March 31, 1971 [21]Appl. No.: 129,749

' [52] US. Cl. ..333/24.1, 333/84 R [51] 'Int. Cl. ..H01p l/32 [58]Field of Search ..333/l.1, 24.1, 24.2, 84 M,

[56] References Cited UNITED STATES PATENTS 3,237,130 2/1966 Cohn..333/10 3,602,845 8/1971 Agrios ..333/24.1 3,350,663 10/1967Siekanowicz et al ..333/1.1

11/1966 Neckenburger ..333/24.2 11/1970 Freibergs ..333/31R OTHERPUBLICATIONS Robinson et al., Slot Line Application To Miniature FerriteDevices, IEEE Trans. on M'IT, Dec. 1969, p. l097-1 101.

Primary Examiner-Paul L. Gensler Attorney-S. C. Yeaton [5 7] ABSTRACT Ahigh frequency gyromagnetic electromagnetic wave transmission device hasa symmetric structure including planar high frequency energy conductorsdefining a wave guiding slot, the conductors being based on a dielectricsubstrate and covered by a similar superstrate, in which the dielectricstrata are formed with gyromagnetic toroids which may be excited toproduce static magnetic bias fields for the control of the velocity ofpropagation of high frequency energy along the transmission device.

1 Claim, 4 Drawing Figures PATENTEI] UECPB I972 33. 707,688

sum 2 0F 2 FERRIMAGNETIC LAYER FIG.4.

I/VI/E/VTORS GERALD H. POBHVSO/V HARRY F. STRENGLEl/V Z1 TTOR/VEYFERRlMAGNETlC LAYER HIGH FREQUENCY GYROMAGNETIC DEVICE EMPLOYING SLOTTRANSMISSION LINE BACKGROUND OF THE INVENTION 1. Field of the InventionThe invention pertains to gyromagnetic devices of the type forcontrolling electromagnetic wave transmission of energy bound to highfrequency energy transmission lines and more particularly relates to asymmetl ric planar slot wave transmission system including gyromagneticmedia for controlling the velocity of propagation of the high frequencyelectromagnetic energy.

2. Description of the Prior Art The operation of gyromagnetic materialssuch as are used in high frequency energy transmission devices is basedupon an interaction between electron spins aligned by a magnetic biasfield and the magnetic field of the propagating electromagnetic wave.The interaction develops when the bias and high frequency magneticfields have components that are orthogonally oriented. Under theseconditions, the magnetic bias field may affect the electromagnetic waveeither reciprocally or non-reciprocally, depending on the polarizationof the high frequency electromagnetic wave. Non-reciprocity usuallyrequires a circularly polarized wave, although certain devices utilizethe principle of Faraday rotation to obtain non-reciprocal operationwith linearly polarized waves. Reciprocal operation, however, requires alinearly polarized electromagnetic wave orthogonally oriented withrespect to the magnetic bias field.

The operation of gyromagnetic devices also depends on the magnitude ofthe bias magnetic field. If the magnitude of the bias field is set at avalue below the gyromagnetic resonance level, the interaction betweenthe bias and high frequency magnetic field produces a change in thephase velocity of the electromagnetic wave as it propagates through thegyromagnetic material. When the magnitude of the bias fields inincreased to the gyromagnetic resonance level, a reciprocal phaseshifter functions as an attenuator or as a reciprocal loss device and anon-reciprocal phase shifter functions as an isolator or non-reciprocalattenuator.

Beside the polarization of the high frequency electromagnetic wave andthe magnitude of the bias magnetic field, the intrinsic characteristicsof the gyromagnetic material are also significant in determining thenature of operation of gyromagnetic circuit component. Materials havinga square hysteresis loop magnetization characteristic readily retaintheir magnetization. Such materials, when constructed in the form oftoroids having closed magnetic paths, have been found useful, forexample, in digital latching phase shifters. Other materials which donot have square hysteresis loop characteristics are not capable ofmaintaining their magnetization. These materials are particularlyuseful, for example, in continuously variable phase shifters and singleside band modulators.

Reciprocal latching digital phase shifters utilize toroids made ofgyromagnetic material and may operate by switching between two differentmagnetization states to provide two discrete values of phase shift.These phase shifters are switched by means of current pulses flowingthrough an electrical conductor threading the toroid aperture. Theswitching may be between two magnetization states of unequal magnitudeor polarity in a single flux path (known as magnitude or collinearswitching), or between two remanent magnetization states in differentbut intersecting flux paths (known as orthogonal or non-collinearswitching). The orthogonal switching technique is free of certainlimitations inherent in the magnitude switching technique which undulycomplicate the driver equipment and restrict the maximum switching rate.For such reasons, orthogonal switching is often used in practice.

Prior art reciprocal latching types of digital phase shifters employingorthogonal switching techniques generally comprise garnet or ferritetoroidal elements with one or more apertures having an axis of symmetrytransverse to the direction of the electromagnetic wave propagation andanother aperture having a longitudinal axis of symmetry parallel to thedirection of the electromagnetic wave propagation. These devices havebeen used within transmission line systems wherein the center conductorof the transmission line threads the longitudinal aperture. Besidesbeing restricted to such transmission line systems, these prior artconfigurations provide closed magnetic paths about the longitudinalaperture that seriously impair latching and fast switching capabilities.

Absent in the prior art are phase control or phase shifting devicesfully suitable for direct incorporation into high frequency andmicrowave integrated circuits. Thus, the inexpensive techniquescurrently used in manufacture of microwave integrated circuits have notbeen beneficially applied in integrated circuits requiring phaseshifters. The prior art has thus not benefitted by the use of planarbalanced phase shifter configurations permitting fully efficientinteraction between the controlling bias magnetic field and the highfrequency propagating wave energy it is to control. Further, prior artdevices generally are characterized by lack of symmetry and permitundesired coupling between the conductors for magnetizing thegyromagnetic material and the high frequency fields they are to control.

SUMMARY OF THE INVENTION The present invention relates to gyromagneticelectromagnetic wave propagation control devices of the type forcontrolling a characteristic of electromagnetic energy transmission inhigh frequency transmission lines. The wave propagation control devicecomprises a symmetric structure including planar high frequency energyconductor strips for defining a wave guiding slot. On each side of theplane of the conducting strips is placed a layer of a gyromagneticsubstance in the fonn of a garnet or ferrite material. Formed within thegyromagnetic layers are toroidal magnetic circuits which may be excitedfor producing cooperating static bias magnetic fields. The latter fieldsare arranged to interact cooperatively with the gyromagnetic material,altering the phase velocity of propagation of electromagnetic energyalong the energy transmission device.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view partiallyin cross section of a balanced slot transmission line as employed in thepresent invention and showing the character of the fields ofelectromagnetic waves propagated therein.

FIG. 2 is a perspective view of a modified portion of the transmissionline of FIG. 1 showing one means for coupling electromagnetic wavesthereto.

FIG. 3 is a cross section view of the embodiment of FIG. 4 taken alongthe lines 3-3 thereof.

FIG. 4 is a perspective view partially in cross section of a preferredembodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Slot transmission line planarwave guides, as known in the prior art, consist of a slot or extendedgap dividing a conductive coating situated on one side of a dielectricor ferrimagnetic substrate into two portions, the other side of thesubstrate generally being bare. With a substrate of suitably highpermittivity, the mode of excitation of the slot transmission line issuch that the traveling wave is closely bound to the region immediatelyadjacent the slot and radiation is minimized. The oscillating electricfield extends generally from one edge of the slot to the other; theoscillating magnetic field lies generally in a plane perpendicular tothe slot. The dominant propagation mode is generally like the TE, modeof propagation in rectangular wave guide.

Most important, the propagating electromagnetic wave has ellipticallypolarized high frequency magnetic field regions as are required for usein microwave gyromagnetic or ferrimagnetic devices, as in nonreciprocalmicrowave devices. The polarized regions are more effectively availablethan in other types of transmission lines. For example, in the case ofmicrostrip transmission line, the meander line configuration must beused to provide regions of elliptical polarization. However, in thatstructure, only a small part of the total transmission line exhibitselliptical polarization which therefore interacts inefficiently with thegyromagnetic or ferrimagnetic material. It is observed thatcharacteristic impedance and phase velocity vary rather slowly withfrequency in slot line.

While a complete system of slot line microwave components may beconstructed as a microwave integrated circuit using only slottransmission line as the interconnecting agency, there are available inthe prior art transition elements between slot line and moreconventional wave guiding elements, such as broad band transitionbetween slot line and coaxial line. Unlike microstrip, slot line doesnot require the use of a grounding plane. Furthermore, slot line is alsoreadily constructed by applying thin metal films to one side of asubstrate and then using conventional photo-etching procedures to formthe slot.

In the present invention, the balanced slot transmission line of FIG. 1is employed; the planar high frequency energy conducting strips 1, 1aare sandwiched between dielectric layers 2, 2a in a manner such as toleave an empty slot 3, in the geometrical center of the laminatedstructure. So as to minimize radiation and to confine the propagatingenergy closely bound to slot 3, the material selected for layers 2, 2apreferably has a high dielectric constant and slot 3 is made relativelynarrow. In this manner, the ratio of guided to free-space wave lengthmay be 0.4 or smaller, though other ratios may be used.

For convenience, the character of the traveling electric field E isrepresented in FIG. 1 at the input plane 4 of the transmission line atan arbitrary time. The electric field E lines form a symmetric patternabout the slot 3, leaving the upper surface of conducting strip 1 atright angles thereto and some passing through dielectric layer 2 tointersect the upper surface of conducting strip la again at right anglesto the latter. Other portions of the electric field symmetrically leaveand reenter the upper surface of dielectric layer 2 before terminatingon strip 1a. The electric field E pattern has mirror image symmetryabove and below the plane of conducting strips 1, la.

In a similar manner, the traveling magnetic field H is shown at anarbitrary time and position with respect to the above representation ofthe electric field E. The magnetic fields form closed loops passingthrough the slot 3. The fields are symmetrical about the plane of theconducting strips 1, 1a and are normal to this plane where they passthrough it.

It will be understood that the balanced slot transmission line mayreadily be constructed by using any of several techniques alreadyestablished for the construction of the various types of planartransmission line, including microstrip transmission line. For example,a suitable dielectric substrate layer 2a may have formed on its surfaceby vacuum or electroless deposition of copper, silver, or gold aconducting thin layer from which slot 3 may be removed by conventionalmechanical or etching processes, thus forming appropriately separatedconducting strips 1, la. To complete the symmetric layered structure,the second dielectric layer 2 may be placed on top of the upper surfacesof conducting strips 1, la and may be held in place by conventionalfasteners or by a suitable adhesive material.

The dielectric material of layers 2, 2a may be any conventional highdielectric constant material such as conventionally used in microwaveintegrated circuit technology. Dielectric constants on the order of 16are often employed. Gyromagnetic or ferrimagnetic materials are foundparticularly suited when the balanced slot transmission line is to beemployed in devices such as electronically adjustable phase shifters.Substances such as yttrium gadolinium iron garnet, including aluminum ordysprosium substituted yttrium gadolinium iron garnet, may be employed.Such materials are described by G. R. Harrison and L. R. Hodges in theUS. Pat. No. 3,l32,l05 for Temperature Compensated Yttrium GadoliniumIron Garnets, issued May 5, 1964 and assigned to the Sperry RandCorporation. Certain other ferrimagnetic materials, such as aluminum ormanganese substituted lithium ferrites also have adequate temperaturestability, square magnetization loop characteristics, and microwavepropagation properties.

As noted previously, large scale microcircuits may be constructed usingbalanced slot transmission line; furthermore, it may be readily coupledto conventional non-balanced slot line or to other types of planar orother wave guides. FIG. 2, for example, illustrates a transition from abalanced slot line comprising conductive strips 1, la and dielectricsheets 2, 2a to a nonbalanced section of slot line where both stripconductors 1, la are present, but only dielectric layer 2a is present. Aconventional matched transition from the non-balanced slot line sectionto a coaxial line having concentric conductors 7, 7a may then be made,with outer conductor 7 soldered at 8 to conducting strip 1 or affixedthereto by a conducting epoxy cement. Inner conductor 7a is bentdownward to provide a conducting region which may be soldered at 8a toconducting strip la. Other types of matched transitions have beendescribed in the literature for coupling non-balanced slot andmicrostrip transmission lines directly through one layer of dielectricsubstrate. The transition or coupling junction is formed by having themicrostrip line cross above the slot at right angles thereto, thedielectric layer being interposed between the lines. The end of themicrostrip line adjacent the coupling junction is open-circuited onequarter of a wave length from the coupling junction and the slot isshort-circuited one quarter of a wave length from the coupling junction.

FIGS. 3 and 4 illustrate an embodiment of the invention in the form of abalanced slot transmission line phase shifter. In FIGS. 3 and 4, thewave guiding function of the apparatus associated with slot 13 comprisesconducting strips 11, 11a forming a layer separating ferrimagneticdielectric layers 12, 12a. Elements 1], 11a, 12, 12a, and 13 cooperatein propagating electromagnetic energy in the same manner as thecorresponding respective elements 1, la, 2, 2a, and 3 of FIG. 1.However, ferrimagnetic elements 12, 12a are each modified to formmagnetic circuit toroids one above the other in a region which performsthe phase shifting function. It will be recognized that various meansmay be employed to inject high frequency energy into and to abstract itfrom the propagation structure of FIGS. 3 and 4, such as that of thearrangement of FIG. 2.

Since ferrimagnetic layers 12 and 12a are similar, the toroidalstructure in the phase shifting region of only one of these elementsrequires description. As seen in FIG. 3, ferrimagnetic layer 12 issupplied with an interior hollow portion formed therein by any wellknown technique. For example, while it is preferred to make the magnetictoroid as an integral element, layer 12 may be made in two parts, onebeing flat and the other having a hollowed-out portion such that whenthe two parts are fixed together, the hollow region 20 is enclosed byferrimagnetic material.

As seen in FIGS. 3 and 4, the hollow region 20 is almost completelyfilled with a sheet composed of nonmagnetic insulator material 21 whichmay have substantially the same dielectric constant as that of theferrimagnetic material. The minor portion of hollow region 20 not filledby dielectric sheet 21 accommodates an electrical conductor wire 22which extends longitudinally along one side of hollow region 20generally parallel to the direction of electromagnetic energytranslation and along substantially all of the toroidal or phaseshifting region. Substantially at the ends of the toroidal region, theends 23 and 24 of wire 22 are bent upwardly and project through holesdrilled in the ferrimagneticlayer 12 so that these may be broughtoutside of the transmission line system for the supply of controlsignals to wire 22, as will be further described.

In a similar manner, the bottom ferrimagnetic layer 6 12a is providedwith an interior hollow region 20a for accommodating a dielectric sheet21a and a longitudinal wire 22a whose ends 23a, 24a pass through thelower or outer surface of ferrimagnetic layer 12a, where wire ends 23a,24a are accessible for the supply of control voltages. The number andplacement of wires such as wires 22 and 22a may vary from that shown, asmay the relative size of the various parts of the phase shifter device.The supply of electrical signals to the wire ends 23, 23a, 24, 24a issuch as to cooperate in producing a controllable amplitude static orbiasing magnetic field of a particular sense in the ferrimagnetic layers12, 12a immediately adjacent slot 13, thus controlling the velocity ofpropagation of energy down the slot transmission line system.

As in conventional high frequency transmission line phase shifters, anyof several types of conventional driving circuits, including analogue ordigital circuits, may be employed to supply currents to wires 22, 22a,including single bit and multiple bit driver circuits. In the single bitdriver combination, for instance, bias magnetic fields in the toroids offerrimagnetic layers 12, 12a are erased by a relatively massive currentimpulse before each commanded setting to saturate the ferrimagneticmaterial fully and to eliminate all memory of its previously heldstates; it is then set by the driver circuit to a predeterminedunsaturated state by a current pulse calibrated according to thecommanded phase shift. Other types of drivers do not drive the materialinto saturation. Since the particular type of driver current source tobe employed does not necessarily constitute a part of the presentinvention, and since conventional driver circuits may satisfactorily beemployed, a detailed description of such driver circuits is not requiredherein.

It is seen that the invention is a novel high frequency phase control orphase shifting device using a balanced slot transmission line loadedsymmetrically by ferrimagnetic circuit toroids. The relative phase ofhigh frequency energy may be varied by changing the level or thedirection of the magnetization of the toroids. The composite structuremay be housed in a suitable enclosure and coupled to a variety ofinput-output transmission line types. Particularly advantageous is thefact that the structure of the slot line wave propagating and phaseshifting system lends itself readily to the use of known techniques nowused in the manufacture of microwave integrated circuits. The symmetryof the system desirably improves efficiency and reduces total size.Latching operation is efficient and the conductors for magnetizing themagnetic circuit toroids are isolated from the high frequency fieldsthey are to control. Driver design is simplified and performanceimproved. Linear characteristics are readily achieved.

While the invention has been described in its preferred embodiments, itis to be understood that the words which have been used are words ofdescription rather than of limitation and that changes within thepurview of the appended claims may be made without departure from thetrue scope and spirit of the invention in its broader aspects.

We claim:

1. A compact high frequency energy phase shifter comprising:

first and second planar high frequency current conducting means lying ina common plane and having a narrow gap therebetween for propagatingtraveling high frequency electric fields therein,

first and second gyromagnetic means symmetrically electrical conductormeans within said thin substantially rectangular closed cavity meanslying therein substantially parallel to the direction of high frequencyfield propagation within said narrow said electrical conductor meansrespectively having extension means passing through said fractional partof said respective gyromagnetic means for the purpose of formingrespective pairs of electrical terminal means exterior thereof, and

high frequency energy coupler means coupled in high frequency energyexchanging relation to said first and second high frequency currentconducting means at least at one end thereof spaced from said fractionalpart of said gyromagnetic means.

1. A compact high frequency energy phase shifter comprising: first andsecond planar high frequency current conducting means lying in a commonplane and having a narrow gap therebetween for propagating travelinghigh frequency electric fields therein, first and second gyromagneticmeans symmetrically disposed on opposed sides of said high frequencycurrent conducting means in contiguous relation therewith forsubstantially covering same while enclosing said narrow gap, each saidgyromagnetic means comprising a temperature stable ferrimagneticmaterial and having thin enclosed substantiallyrectangular closed cavitymeans lying substantially parallel to and spaced symmetrically from saidcommon plane and being substantially filled with non-magnetic materialhaving a dielectric constant substantially equal to the dielectricconstant of said ferrimagnetic material for defining closed magneticcircuit means in a fractional part of said gyromagnetic means,electrical conductor means within said thin substantially rectangularclosed cavity means lying therein substantially parallel to thedirection of high frequency field propagation within said narrow gap,said electrical conductor means respectively having extension meanspassing through said fractional part of said respective gyromagneticmeans for the purpose of forming respective pairs of electrical terminalmeans exterior thereof, and high frequency energy coupler means coupledin high frequency energy exchanging relation to said first and secondhigh frequency current conducting means at least at one end thereofspaced from said fractional part of said gyromagnetic means.